Code in both pages identical.
why do you use different files with identical code?
the 'problem' lies in the way, Twenty Eleven deals with the sidebar formatting by adding the body_class
.singular to templates without sidebar.
for the 'sidebar-page.php' template, there is a part in the code that does not add the body_class
in your child theme, you need to 'remove' this css class
.singular for for any page templates that use the sidebar;
btw: your front page also has display problems (at least in FF3.6) possibly caused by one or more of these validation errors: